Shikimate and folate pathways in the protozoan parasite, Perkinsus olseni

In vivo and in vitro evaluation of the effect of glyphosate (Roundup) on Toxoplasma gondii

Apicoplast, a derived non-photosynthetic plastid, which is found in most Apicomplexa, provides essential functions to parasites. The shikimate pathway is localized in the plant chloroplast as a remarkable route for the survival of the Toxoplasma. In this study, in vivo and in vitro effects of glyphosate (Roundup, Herbicide), as an inhibitor of the enzyme, were evaluated on T. gondii. Tachyzoites of RH strain were incubated for 1.5 h in various concentrations (1-128 µg/ml) of glyphosate. The parasite was cultivated in the cell monolayer of the heLa cell, and then the cultures were exposed to various concentrations. To evaluate the therapeutic quality, 2 × 10⁵ tachyzoites were intradermally inoculated into ten mice from each group. Four doses of the compound were daily administrated every 24 h after inoculation due 10 days continuously. Also, two other groups were assigned as the positive and negative control. In flow cytometry, the highest mortality rate was related to concentrations of 128 and 256 μg/ml, 18.29% and 18.64%, respectively, while the mortality rate was 0.03% in the negative control (P value > 0.05). Based on microscopic observation of the stained touch smear of the liver, all treated mice were killed by the parasite. This compound also had no lethal effect on the mice. According to the results of this study, glyphosate is not a good candidate for the treatment of toxoplasmosis. It seems that the parasite has another pathway for providing the essential amino acids.

New insights into the Manila clam - Perkinsus olseni interaction based on gene expression analysis of clam hemocytes and parasite trophozoites through in vitro challenges

The Manila clam (Ruditapes philippinarum) is the bivalve species with the highest global production from both fisheries and aquaculture, but its production is seriously threatened by perkinsosis, a disease caused by the protozoan parasite Perkinsus olseni. To understand the molecular mechanisms underlying R. philippinarum-P. olseni interactions, we analysed the gene expression profiles of in vitro challenged clam hemocytes and P. olseni trophozoites, using two oligo-microarray platforms, one previously validated for R. philippinarum hemocytes and a new one developed and validated in this study for P. olseni. Manila clam hemocytes were in vitro challenged with trophozoites, zoospores, and extracellular products from P. olseni in vitro cultures, while P. olseni trophozoites were in vitro challenged with Manila clam plasma along the same time-series (1 h, 8 h, and 24 h). The hemocytes showed a fast activation of the innate immune response, particularly associated with hemocyte recruitment, in the three types of challenges. Nevertheless, different immune-related pathways were activated in response to the different parasite stages, suggesting specific recognition mechanisms. Furthermore, the analyses provided useful complementary data to previous in vivo challenges, and confirmed the potential of some proposed biomarkers. The combined analysis of gene expression in host and parasite identified several processes in both the clam and P. olseni, such as redox and glucose metabolism, protease activity, apoptosis and iron metabolism, whose modulation suggests cross-talk between parasite and host. This information might be critical to determine the outcome of the infection, thus highlighting potential therapeutic targets. Altogether, the results of this study aid understanding the response and interaction between R. philippinarum and P. olseni, and will contribute to developing effective control strategies for this threatening parasitosis.

Amino Acid Uptake and Metabolism of Legionella pneumophila Hosted by Acanthamoeba castellanii

Legionella pneumophila survives and replicates within a Legionella-containing vacuole (LCV) of amoebae and macrophages. Less is known about the carbon metabolism of the bacteria within the LCV. We have now analyzed the transfer and usage of amino acids from the natural host organism Acanthamoeba castellanii to Legionella pneumophila under in vivo (LCV) conditions. For this purpose, A. castellanii was 13C-labeled by incubation in buffer containing [U-(13)C(6)]glucose. Subsequently, these 13C-prelabeled amoebae were infected with L. pneumophila wild type or some mutants defective in putative key enzymes or regulators of carbon metabolism. 13C-Isotopologue compositions of amino acids from bacterial and amoebal proteins were then determined by mass spectrometry. In a comparative approach, the profiles documented the efficient uptake of Acanthamoeba amino acids into the LCV and further into L. pneumophila where they served as precursors for bacterial protein biosynthesis. More specifically, A. castellanii synthesized from exogenous [U-13C6]glucose unique isotopologue mixtures of several amino acids including Phe and Tyr, which were also observed in the same amino acids from LCV-grown L. pneumophila. Minor but significant differences were only detected in the isotopologue profiles of Ala, Asp, and Glu from the amoebal or bacterial protein fractions, respectively, indicating partial de novo synthesis of these amino acids by L. pneumophila. The similar isotopologue patterns in amino acids from L. pneumophila wild type and the mutants under study reflected the robustness of amino acid usage in the LCV of A. castellannii.

Quantitative assessment of the proliferation of the protozoan parasite Perkinsus marinus using a bioluminescence assay for ATP content

Perkinsus marinus is a protozoan parasite that causes "Dermo" disease in the eastern oyster Crasssostrea virginica in coastal areas of the USA. Until now, intervention strategies against the parasite have found limited success, and Dermo still remains one of the main hurdles for the restoration of oyster populations. We adapted a commercial adenosine tri-phosphate (ATP) content-based assay to assess the in vitro proliferation of P. marinus in a 96-well plate format, and validated the method by measuring the effects of potential anti-proliferative compounds. The sensitivity (1.5-3.1 × 10(4) cells/well), linearity (R (2) = 0.983), and signal stability (60 min) support the reliability of the assay for assessing cell proliferation. Validation of the assay by culturing P. marinus in the presence of increasing concentrations of triclosan showed a dose-response profile. The IC50 value obtained was higher than that reported earlier, possibly due to the use of different viability assay methods and a different P. marinus strain. The antibiotics G418 and tetracycline and the herbicide fluridone were active against P. marinus proliferation; the IC50 of chloramphenicol, ciprofloxacin, and atrazine was relatively high suggesting either off-target effects or inability to reach the targets. The validation of the ATP-based assay, together with significant advantages of the Perkinsus culture methodology (homogeneity, reproducibility, and high cell densities), underscores the value of this assay for developing high-throughput screens for the identification of novel leader compounds against Perkinsus species, and most importantly, for the closely-related apicomplexan parasites.

The search for the missing link: a relic plastid in Perkinsus?

Perkinsus marinus (Phylum Perkinsozoa) is a protozoan parasite that has devastated natural and farmed oyster populations in the USA, significantly affecting the shellfish industry and the estuarine environment. The other two genera in the phylum, Parvilucifera and Rastrimonas, are parasites of microeukaryotes. The Perkinsozoa occupies a key position at the base of the dinoflagellate branch, close to its divergence from the Apicomplexa, a clade that includes parasitic protista, many harbouring a relic plastid. Thus, as a taxon that has also evolved toward parasitism, the Perkinsozoa has attracted the attention of biologists interested in the evolution of this organelle, both in its ultrastructure and the conservation, loss or transfer of its genes. A review of the recent literature reveals mounting evidence in support of the presence of a relic plastid in P. marinus, including the presence of multimembrane structures, characteristic metabolic pathways and proteins with a bipartite N-terminal extension. Further, these findings raise intriguing questions regarding the potential functions and unique adaptation of the putative plastid and/or plastid genes in the Perkinsozoa. In this review we analyse the above-mentioned evidence and evaluate the potential future directions and expected benefits of addressing such questions. Given the rapidly expanding molecular/genetic resources and methodological toolbox for Perkinsus spp., these organisms should complement the currently established models for investigating plastid evolution within the Chromalveolata.

The use of parasites as bioindicators of pesticide exposure

Organisms used in risk assessment of pesticides must be the most sensitive ones to pesticides exposure. The aim of this study was to observe the effect of two commercial pesticide products (containing glyphosate and tolylfluanid) to larval stages of parasites Cooperia curticei, Ostertagia circumcincta, Haemonchus contortus and Trichostrongylus axei. There were two concentrations tested for each product vs. control group. Larvae (500 individuals/Petri dish) were incubated at 27 °C and observed daily for 42 days.

We found out that T. axei larvae are the most resistant ones to tolylfluanid exposure – there was no statistical significance in any concentration tested after 42 days of tolylfluanid exposure. 100% of dead larvae were found on 33^rd day of experiment at higher concentration, resp. on 37^th day at lower tested concentration of glyphosate. C. curticei, O. circumcincta and H. contortus showed similar statistical significance in both pesticides tested (there was high statistical significance (p<0.0001) at both concentrations of glyphosate and only at higher tested concentration of tolylfluanid). C. curticei and H. contortus larvae were found dead, spiral shaped and without movement at all concentrations tested, spiral shape was not observed in other two tested larvae. O. circumcincta larvae reacted to pesticides exposure very quickly; rapid death was recorded on second day of experiment at both concentrations of glyphosate and at higher tested concentration of tolylfluanid. From four tested small ruminant parasites (L3), O. circumcincta larvae seem to be the most sensitive ones and need further research.

Identified biosynthetic pathway of aspergiolide A and a novel strategy to increase its production in a marine-derived fungus Aspergillus glaucus by feeding of biosynthetic precursors and inhibitors simultaneously

Aspergiolide A is a novel anti-tumor anthraquinone derivant produced by marine-derived fungus Aspergillus glaucus. To identify its biosynthetic pathway and further improve the production, the effects of biosynthetic pathway specific inhibitors and precursors were investigated. Cerulenin and iodoacetamide, the specific inhibitors of polyketide pathway, could completely inhibit the aspergiolide A accumulation. Putative precursors of polyketide pathway could increase aspergiolide A production greatly, such as 6 mM acetate increased production by 135%. Simvastatin and citrate, the inhibitors of mevalonate pathway, stimulated the production by 63% and 179%, respectively. Considering that acetyl-CoA is the common starter unit in both polyketide and mevalonate pathway, a novel strategy was designed to stimulate the aspergiolide A accumulation. Combinations of 12 mM acetate with 0.3 mM simvastatin could increase the production by 151%, while the supplementation with 12 mM acetate and 12 mM citrate brought a 262% increase of aspergiolide A production. The strategy might be very useful to enhance the production of other secondary metabolites derived from polyketide pathway.

Effect of the herbicide Roundup on Perkinsus olseni in vitro proliferation and in vivo survival when infecting a permissive host, the clam Ruditapes decussatus

Coastal habitats are increasingly being exposed to herbicide contamination from urban and agricultural catchments. Data on its toxicity on aquatic ecosystems, especially those based on sediment, are relatively scarce. This study aimed at investigating whether the susceptibility of an aquatic filter-feeding organism, the carpet-shell clam (Ruditapes decussatus) to the parasite Perkinsus olseni was influenced by the herbicide Roundup and its active ingredient glyphosate. The effect of Roundup and glyphosate on P. olseni in vitro proliferation was also evaluated and appeared to confirm the higher toxicity of Roundup when compared with technical grade glyphosate.

The effects of several common anthropogenic contaminants on proliferation of the parasitic oyster pathogen Perkinsus marinus

Estuarine contaminants have varying effects on estuarine inhabitants and host-parasite interactions. Some field collected contaminant mixtures have been shown to increase oyster susceptibility to parasitism by Perkinsus marinus, but little is known about contaminant effects on the parasite itself. This study examined the effects of ammonium, nitrate, phosphate, fluoranthene, phenanthrene and a common herbicide mixture (Weed-B-Gone) on in vitro proliferation of P. marinus. Only the herbicide had a significant effect, but not at or below the manufacture's recommended application rate (7.81 microl ml(-1)). The herbicide's active ingredients (3.1% 2,4-dichlorophenoxyacetic acid, 10.6% mecoprop and 1.3% dicamba) mimic growth hormones of broadleaf plants; over stimulation of growth results in death. The mode of action of these compounds on P. marinus warrants further investigation which may provide insight towards the identification of biocides to control P. marinus.

Evolutionary origins of the eukaryotic shikimate pathway: gene fusions, horizontal gene transfer, and endosymbiotic replacements

Currently the shikimate pathway is reported as a metabolic feature of prokaryotes, ascomycete fungi, apicomplexans, and plants. The plant shikimate pathway enzymes have similarities to prokaryote homologues and are largely active in chloroplasts, suggesting ancestry from the plastid progenitor genome. Toxoplasma gondii, which also possesses an alga-derived plastid organelle, encodes a shikimate pathway with similarities to ascomycete genes, including a five-enzyme pentafunctional arom. These data suggests that the shikimate pathway and the pentafunctional arom either had an ancient origin in the eukaryotes or was conveyed by eukaryote-to-eukaryote horizontal gene transfer (HGT). We expand sampling and analyses of the shikimate pathway genes to include the oomycetes, ciliates, diatoms, basidiomycetes, zygomycetes, and the green and red algae. Sequencing of cDNA from Tetrahymena thermophila confirmed the presence of a pentafused arom, as in fungi and T. gondii. Phylogenies and taxon distribution suggest that the arom gene fusion event may be an ancient eukaryotic innovation. Conversely, the Plantae lineage (represented here by both Viridaeplantae and the red algae) acquired different prokaryotic genes for all seven steps of the shikimate pathway. Two of the phylogenies suggest a derivation of the Plantae genes from the cyanobacterial plastid progenitor genome, but if the full Plantae pathway was originally of cyanobacterial origin, then the five other shikimate pathway genes were obtained from a minimum of two other eubacterial genomes. Thus, the phylogenies demonstrate both separate HGTs and shared derived HGTs within the Plantae clade either by primary HGT transfer or secondarily via the plastid progenitor genome. The shared derived characters support the holophyly of the Plantae lineage and a single ancestral primary plastid endosymbiosis. Our analyses also pinpoints a minimum of 50 gene/domain loss events, demonstrating that loss and replacement events have been an important process in eukaryote genome evolution.